Polyphenylene ethers are a well-known class of polymers characterized by a unique combination of chemical, physical and electrical properties over a temperature range of more than 350.degree. C. extending from a brittle point of about -170.degree. C. to heat distortion distortion temperature of 190.degree. C. This combination of properties renders them suitable for use as engineering thermoplastics in a broad range of applications which are well known in the art and are disclosed in numerous patents and other publications.
In recent years, there has been considerable interest in combining polyphenylene ethers with other resins to produce compositions with even more advantageous properties. For example, polymers such as polyamides are frequently noted for their solvent resistance and blends of such polymers with polyphenylene ethers might be expected to possess the advantageous properties of the latter and in addition be highly resistant to solvents. However, simple blends of polyphenylene ethers and polyamides are generally incompatible, frequently undergoing phase separation and delamination. They typically contain large, incompletely dispersed polyphenylene ether particles and no phase interaction between the two resin phases.
U.S. Pat. No. 4,642,358 describes the reaction of polyphenylene ethers with such polycarboxylic reactants as trimellitic anhydride acid chloride (TAAC).
A disadvantage of the reaction of polyphenylene ethers with TAAC is that it must be conducted in solution, typically in an organic solvent such as toluene. Polyphenylene ethers are often melt processed rather than solution processed, in which case the requirement of solution functionalization is undesirable. Moreover, the products prepared by this method frequently coagulate, contain large proportions of fines and have substantial chloride content. All of these conditions may be disadvantageous for many utilities of the resulting blends.
In U.S. Pat. No. 4,808,671, there is described the reaction of polyphenylene ethers with 4-esters of trimellitic anhydride in the presence of a catalytic amount of at least one triaryl phosphite. This process may be conducted in the melt and may utilize such trimellitic acid esters as the 4-(o-carbophenoxyphenyl) ester, also known as the 4-(phenylsalicylate) ester, of trimellitic anhydride. Esters of this type react with polyphenylene ethers in two ways: by functionalizing it with functionality derived from the 4-ester of trimellitic anhydride and by capping unfunctionalized molecules with salicylate in accordance with U.S. Pat. No. 4,760,118. The disadvantage of this method is the requirement for triaryl phosphite catalysis in order to promote complete reaction. In the absence of triaryl phosphite, the functionalization reaction is incomplete and substantial proportions of residual trimellitic anhydride 4-ester may remain in the production, with possible detrimental results.
U.S. application Ser. No. 07/474,880, filed Feb. 2, 1990, discloses a method of producing a dicarboxylate-capped polyphenylene ether capable of forming blends with polyamides having high impact and tensile strength. The above-mentioned dicarboxylate-capped polyphenylene ethers are prepared by melt blending with application of vacuum at least one polyphenylene ether with at least one trimellitic anhydride salicylate ester.
However, the trimellitic anhydride salicylate ester starting material must be solution synthesized and is not economically obtained. It would be preferable to use commercially available starting material capable of providing anhydride functionality onto polyphenylene ethers.
Therefore, the present invention provides economically obtainable new materials that do not have a cyclic anhydride as a functional group but rather have a combination of carboxylic acids, salicylate esters, and some linear anhydrides thus providing a polymer blend having more oxidative stability.